This disclosure relates to a refrigerant compressor with a magnetic bearing assembly and a variable speed electric motor. More particularly, the disclosure relates to such a refrigerant compressor having a variable geometry diffuser.
Refrigerant compressors are used to circulate refrigerant to a chiller via a refrigerant loop. One type of typical refrigerant compressor operates at fixed speed and has a set of variable inlet guide vanes arranged upstream from the impeller. The variable inlet guide vanes are actuated during operation of the refrigerant compressor to regulate its capacity during various operating conditions.
Some fixed speed refrigerant compressors have additionally employed a variable-geometry diffuser downstream from the compressor to improve capacity control during the various operating conditions.
Fixed-speed centrifugal compressors benefit from having both a variable-geometry diffuser and variable-geometry inlet guide vanes. Compressor part-load efficiency and stable operating range both improve. For fixed-speed centrifugal compressors stable operating range is limited without the addition of a variable-geometry diffuser while off-design efficiency suffers without the addition of a set of inlet guide vanes.
This disclosure describes a centrifugal compressor capacity control apparatus and method using a variable-speed compressor with a variable-geometry diffuser that improves the stable operating range or turn-down capability of the compressor and results in higher compressor efficiency than a variable speed compressor with inlet guide vanes.